The present invention relates to sail apparatus for propelling a body over a solid surface. In particular, the invention relates to conventional sail structures which may be used to propel a ski, skate, iceboat or the like over the ground.
Numerous sail structures are known which are intended to propel a person over solid ground (including ice and snow) using some kind of body member as a means of transport. The U.S. Pat. No. 3,982,766 to Budge discloses a conventional triangular sail intended for use with a skateboard. In this sail structure the horizontal boom is relatively low and extends outward only to one side (i.e., rearward) of the mast. Consequently, the boom cannot be conveniently held and manipulated and it requires considerable force to maintain its attitude with respect to the wind.
The U.S. Pat. No. 3,487,800 to Schweitzer et al. discloses a similar sail configuration for iceboats and other land vehicles. Although the boom in this case has been raised to a more convenient height, it still requires the application of a constant and substantial force to maintain its attitude with respect to the wind. In addition, as in the case with the skateboard sail in the U.S. Pat. No. 3,982,766, the sail is completely opaque and therefore blocks the view of the user.
The U.S. Pat. No. 3,455,261 and 3,830,512 disclose sail structures which are held directly by the user. Because these structures do not include a mast, the user must expend considerable strength in maintaining the sail in position. To some extent, the user himself thus forms the "mast" for the sail.